Suction dredges normally have a downwardly and forwardly inclined ladder carrying a suction pipe which has a suction mouth at its lower end and a rotatable cutter head just forward of such mouth. The head normally is driven by a shaft extending along the ladder from a motor on the upper end of the ladder. Usually the cutter head has a plurality of angularly spaced, toothed ribs spiralling rearwardly from the forward end of the drive shaft. When sand or muck is being dredged, no problems normally arise. When the cutter head is working in hard lumpy clay, sandstone, coral, or other fossil or rock formations, however, problems are encountered in the production of large hard lumps that pass through the cutter head and are large enough to clog or damage the suction and discharge lines and the dredge pump. Clogging or stopping of the lines necessitates time consuming down-time clean-out operations. Pump damage necessitates expensive down-time replacement or repair.